This invention relates to a device for generating an atomic cloud, to a method of generating the atomic cloud, to an apparatus for spectro-scopically analysing a substance which includes the device, and to a method of spectro-scopically analysing a substance which includes the method according to the invention of generating an atomic cloud.
In order to qualitatively or quantitatively analyse substances by spectroscopic techniques, either by detecting emission or absorption of characteristic radiation, it is necessary to generate an atomic cloud. Further, with emissive techniques utilising fluorescence of the atomic cloud, it is desirable that the atomic cloud has a low value of inherent radiation.
It is an object of the present invention to provide a device which generates a suitably dense atomic cloud which preferably has a low value of inherent radiation.
Accordingly, the invention provides a device for generating an atomic cloud which includes
A housing having an inlet and an outlet port through which a gas may be introduced into and removed from the housing; PA1 A cathode having a discharge surface located within the housing; PA1 An anode also located within the housing, spaced from and electrically insulated from the cathode and located such that a discharge may occur between the discharge surface of the cathode and the anode; and PA1 A gas flow directing means for directing a flow of the gas from the inlet port outwardly away from or past the cathode discharge surface, such that, in use, when a suitable potential is applied across the anode and the cathode a glow discharge occurs between the anode and the cathode discharge surface. PA1 Providing a device for generating an atomic cloud which has an anode and a cathode having a discharge surface located within a gas-tight housing; PA1 Applying a suitable potential across the anode and the cathode; and PA1 Causing a gas to flow outwardly away from or past the surface, such that a glow discharge occurs between the anode and the cathode. PA1 generating an atomic cloud of an element, the concentration whereof in the substance is to be determined, in accordance with the method of the invention; PA1 irradiating the atomic cloud with radiation emitted by the substance; and PA1 detecting the amount of fluorescent radiation emitted by the atomic cloud.
Further according to the invention, there is provided a method of generating an atomic cloud, which includes
The gas flow directing means may be such that in use, atoms ejected from the cathode discharge surface are drawn by the gas flow away from the cathode discharge surface to a region beyond the cathode glow region. Thus, the gas may be caused to flow past the periphery of the cathode discharge surface, and/or the cathode may be provided with a passage which has its outlet opening in the cathode discharge surface, such that the gas flows through the passage and out through its outlet opening.
In order to cause the gas to flow past the periphery of the cathode discharge surface, the device may include a gas flow constraining element which is hollow, the cathode being located therein. Preferably, this constraining element is of an electrically insulating material.
The flow rate of the gas may be at a suitable value to ensure a suitable pressure within the housing. Further, the device may be operated at a constant potential difference between the anode and the cathode, or the discharge current between the anode and the cathode may be maintained at a constant value.
The cathode discharge surface may be planar or it may be dished to provide a pseudo-hollow cathode.
In use, a normal or an abnormal glow discharge may occur between the anode and the cathode discharge surface.
The housing may have at least two windows. These windows may be located on optical axes that are mutually orthogonally disposed and which intersect in the region beyond the cathode glow region to which the atoms are drawn by the gas flow. Radiation may enter the device through one of these windows, with resulting fluorescent radiation leaving the device via the other window. In order to minimize the amount of background radiation leaving the housing via the said other window, a region having a low reflectivity may be disposed on the optical axis of the entrance window on the opposite side of the region to which the atoms are drawn to the said window.
The device may have more than one cathode, the cathodes having different chemical compositions. Further in regard to the cathodes, the entire cathodes or at least a portion thereof may be easily replaceably removable.
The anode may have any suitable shape and configuration. It may for example be a rod, pin, plate, or the like.
The anode may be to one side of the cathode discharge surface. Thus, it may be laterally displaced from the line connecting the cathode discharge surface to the region to which the atoms are drawn by the gas flow.
In a particular embodiment, the cathode may be cylindrical, the gas flow being directed along the cylindrical wall thereof past an end wall thereof which constitutes the cathode discharge surface.
The gas may be an inert gas, such as argon.
The invention extends further to an apparatus for spectroscopically analysing a substance, which includes a device for generating an atomic cloud in accordance with the invention.
Still further according to the invention there is provided a method of spectroscopically analysing a substance, which includes